A simple absorbing boundary algorithm for the FDTD method with arbitrary incidence angle

An algorithm was developed by X. Zhang and K.K. Mei (1988) for simulating the propagation of the quasi-TEM wave in a microstrip structure with the wave impinging at normal incidence onto the absorbing boundary. The amount of reflection was reported to be on the order of 3 to 5%. For the present work, the authors rationalize the concept of the absorbing boundary for the finite-difference time-domain (FDTD) method in terms of phase and group velocities, improve on the algorithm with a resulting decrease of two orders of magnitude in the amount of reflection at the tuning frequency, and generalize the algorithm to encompass the case of arbitrary incidence angle. Yet, the algorithm remains very simple and very local, requiring the knowledge of the field values at points located only one space increment away from the absorbing boundary.<>